Recently there have been developed various video signal recorder that code and compress video signals of digital data by a specified mode and perform a digital recording. It is, however, required much expenses and labor for the standardization of compression modes and compressed algorithm hardware, e.g., LSI. In order to reduce the development costs for early development, it is preferable to apply a known standard and its corresponding accumulated techniques, a known hardware of compressed algorithms and the like. Hence there have been developed novel video signal recorders depending on the purpose.
For example, the mode employing 411 digital video signal in which the ratio of luminance signal, chrominance signal and another chrominance signal is 4:1:1, is widely used in general apparatuses for domestic use. While, depending on the purpose, 422 digital video signal containing more chrominance signal may be more preferable in terms of image quality and the like. There have been developed apparatuses that can treat 422 digital video signal by applying the standards and hardware of algorithms for 411 digital video signal.
FIGS. 13(a) to 13(d) are diagrams illustrating the construction of the signal. FIG. 13(a) shows 411 digital video signals that is generally used. FIG. 13(b) shows 422 digital video signal used when high image quality is required. In Figures, "Y" indicates luminance signal, "V" and "U" indicate chrominance signal.
In order to apply such apparatuses as developed in the standard for 411 digital video signal to 422 digital signal, the following processing is performed. That is, 422 digital video signal as shown in FIG. 13(b) are split into 211 digital video signal, which signal are then appended with dummy signal to create pseudo-411 digital signal as shown in FIG. 13(d), followed by necessary processing. The signal shown in FIG. 13(d) has the same format as that of FIG. 13(a), allowing to apply the apparatus with the standard for 411 digital video signal. The two split signals are to be synthesized when recording or regenerating.
A description will be given of a conventional video signal recorder and a video signal regenerator, each treating 422 digital signal as described.
Referring to FIG. 12(a), there is shown the construction of the conventional video signal recorder. A video signal splitter 1001 splits 422 digital video signal with luminance signal to chrominance signal ratio of 4:2:2 into two 211 digital video signals with that ratio of 2:1:1, based on a specified split format. A video signal converter 1002 adds a specified dummy signal into the luminance signal in the input 211 digital video signal to convert it into 411 digital video signal with the luminance signal to chrominance signal ratio of 4:1:1. A high-efficiency coding apparatus 1003 performs a specified high-efficiency coding of the input 411 digital video signal to create compressed data. An error correction coding apparatus 1004 appends a specified error correction coded data to the compressed data. A recorder 1005 records the output of the error correction coding apparatus 1004 in a recording media 1006, e.g., tape media such as VTRs, disk media such as optical disks. In the recording media 1006, digitized data is recorded for the retention.
The video signal recorder so constructed will perform the aforesaid compression, coding and recording as follows. The video signal splitter 1001 abolishes, from the input video signal, portions other than a significant area as a processing object, and then splits 422 digital video signal with the luminance signal to chrominance signal ratio of 4:2:2, into two 211 digital video signal with that ratio of 2:1:1, based on a specified split format. The two split 211 digital video signal are separately input into either of the two video signal converters 1002.
Each video signal converter 1002 appends a specified dummy signal to the luminance signal in the input 211 digital video signal, to convert it into 411 digital video signal with the luminance signal to chrominance signal ratio of 4:1:1. The data of the 211 digital video signal is sequenced in this order: luminance signal (Y), luminance signal (Y), chrominance signal (V), and chrominance signal (U), as shown in FIG. 13(c). The above data is then converted into 411 digital video signal with the sequencing of the luminance signal (Y), dummy signal (D), the luminance signal (Y), dummy signal (D), the chrominance signal (V), and the chrominance signal (U), as shown in FIG. 13(d). All the dummy signal (D) are identical data. Each video signal converter outputs the converted 411 digital video signal to the high-efficiency coder 1003.
Each coder 1003 performs a high-efficiency coding of the input 411 digital video signal by employing a specified high-efficiency coding algorithm, and then outputs it as compressed data.
Referring to FIGS. 14(a) and 14(b), the format of the compressed data will be exemplified. The coder 1003 inherently performs a high-efficiency coding of 411 digital video signal by the algorithm utilizing DCT(discrete cosine transform). A DCT block consists of 8.times.8 pixels. A macro block consists of four DCT blocks of luminance signal (Y), one DCT block of chrominance signal (V) and one DCT block of chrominance signal (U). The compressed data of this macro block is sequenced as shown in FIG. 14(a). The sequence of each DCT block is first DC components, then additional information data, and AC components. In this example, since there is employed pseudo-411 digital signal based on 422 digital signal, the sequence of the DCT block is as shown in FIG. 14(b), and that of the block of the dummy signal (D) is first a specified DC components, then additional data and finally EOB (end of block).
Each coder 1003 outputs such compressed data as shown in FIG. 14(b) to the error correction coder 1004. Each coder 1004 appends error correction codes to the input compressed data by a specified mode to obtain the error correction coded data, and outputs it.
The recorder 1005 records the error correction coded data in a specified position of a specified recording media 1006. Thus, the conventional video signal recorder codes/compresses 422 digital video signal and then records it.
It is noted that the video signal recorder may have two recorders 1005 which separately write in the recording media 1006, as shown in FIG. 12(a), or may have a synthesizer 1007 that synthesizes two output results and then write in the recording media 1006. The operation of the latter is the same as that of the former, except the synthesize and the writing.
Referring to FIG. 15, there is shown the construction of a conventional video signal recorder, in which video data as recorded in the above manner is regenerated to obtain videos. A recording media 1006 is to be recorded video data (error correction coded data) in the conventional video signal recorder, as previously described. A regenerator 2001 regenerates the error correction coded data from the recording media 1006. An error correction decoder 2002 performs the error corrections based on the error correction codes added in the video signal recorder to obtain compressed data, and then outputs it. A high-efficiency decoder 2003 performs the reverse conversion of the high-efficiency coding performed by the video signal recorder to decode digital video signal. A video signal separator 2004 separates the dummy signal added in the video signal recorder out of 411 digital video signal (luminance signal to chrominance signal ratio is 4:1:1) which has been decoded by the high-efficiency decoder 2003, to output 211 digital video signal (luminance signal to chrominance signal ratio is 2:1:1). A video signal synthesizer 2005 synthesizes 211 digital video signal output from two video signal separators 2004, based on a specified synthetic format, thereby obtaining 422 digital video signal with luminance signal to chrominance signal ratio of 4:2:2.
The video signal regenerator so constructed will regenerate the data recorded in the recording media as follows.
The regenerator 2001 regenerates the error correction coded data recorded in a specified position of the recording media 1006. The error correction decoder 2002 performs the error correction based on the error correction codes added in the video signal recorder to output compressed data. The high-efficiency decoder 2003 decodes the compressed data by performing the reverse conversion of the high-efficiency coding in the video signal recorder, to output it as 411 digital video signal. The video signal separator 2004 separates the dummy signal added by the video signal recorder from the 411 digital video signal decoded by the high-efficiency decoder 2003, to output the 211 digital video signal. The video signal synthesizer 2005 synthesizes, based on the synthetic format, the 211 digital video signals as the outputs of the two vide signal separators 2004 to obtain the 422 digital video signal, and then outputs it. The separated dummy signal is to be discarded.
As described above, the conventional video signal recording apparatus and video signal regenerating apparatus are for recording and regenerating 422 digital video signal, respectively, according to the standards and devices basically for 411 digital video signal.
It should be noted that in the conventional video signal recording apparatus dummy signal is added to the original video signal, while in the conventional video signal regenerating apparatus the dummy signal is separated and then discarded. Such useless data treatment in the recording and transmission of video signal will decrease the efficiency. Particularly on recording media, dummy signal requires a storage capacity like video signal. This will cause disadvantages to the effective use of recording media.
When obtaining digital data to be treated by computers and the like, based on the video signal of such as TV signal, it is general that image data comprising digitized video signal is first obtained, the image data is then compressed and coded, and the obtained data is recorded or transmitted. The digitized image data is in a sequence of pixel data having pixel values indicating luminance and chrominance, and the image data is coded by processing to obtain coded image data.
As a general method for compressing/coding image data based on video signal, there is predictive coding. The predictive coding is a system in which a predictive value for an input pixel that is the object of coding is generated, and a difference value between the input pixel and the predictive value is subjected to non-linear quantization, the obtained data is then transmitted. When the image from video signal is treated, a predictive value is obtained by predicting a pixel value at a certain point, from its periphery pixels, based on that adjacent parts tends to have the same or an approximate pixel value indicating luminance and chrominance. The predictive coding has the advantages that the circuit scale for an apparatus is small and the compression rate is low. When data rate after compression is high, high-quality image is obtainable. This is the reason why the predictive coding has been widely used.
FIG. 43 is a conceptual diagram explaining the linear processing and non-linear processing in quantization. Input data has a certain dynamic range. That is, the input data is represented in the range of d-bit as a dynamic range, and, the linear processing is possible. When n-bit output data is obtained by quantizing the input data, a suitable number of quantization representative values are selected, and quantizing values are allocated to the representative values. To each input data, there is given a quantizing value allocated to a quantization representative value that is approximate to the input data. By setting the number of the quantization representative values to not more than 2.sup.2n, the output data can be treated by n-bit.
As shown in FIG. 43, to set quantization representative values at uniform intervals is linear quantization. When an expected value is previously obtained as in the predictive coding, non-linear quantization in which the quantization representative values are set densely in the vicinity of the expected value, and widely as the distance from the expected value is increased.
In FIG. 43, there is shown a rounding processing of from 3-bit to 2-bit. By setting four (2.sup.2) quantization representative values against eight (2.sup.3) ones, the output data can be represented by 2-bit.
In the linear processing, the quantizing representative values are set, for example, by selecting every other piece, to assign the quantizing value. For input data having the values from 0 to 7, they are replaced with the adjacent quantizing representative value to give a quantizing value assigned to the respective representative value in the following manner. For the value of 0 or 1, its quantizing representative value is 0, for the value of 2 or 3, its quantizing value is 2, and the like.
In the non-linear processing, when an expected value for the input data is 3, for example, the setting of quantizing values will be set densely in the vicinity of 3, and roughly as the distance from 3 is increased. As the quantizing width is creased, that is, as the interval of the quantizing representative values is increased, the number of data replaceable with the quantizing representative value is increased. This shows that data of different value tends to be treated equally. Therefore, nearer the vicinity of the expected value, the magnitude of the quantizing value reflects more precisely the magnitude of the input value.
The non-linear quantization utilized in the predictive coding is performed in various systems. Since it is normally difficult to perform the non-linear quantization by such a simple operation as in the linear quantization, that is performed by referring to a table such as a ROM table. This might increase the circuit scale and the processing costs, resulting in the cost increase and the reduced processing speed.
On the other hand, the predictive coding has the problem that transmitted data is a difference value between an input value and a predictive value and, when an error of the predictive value occurs, such an error will be propagated at the regeneration. Thus in order to suppress such an error propagation within a certain range, there has been employed a method of inserting a PCM value periodically. This method, however, decreases the compression rate and causes the unevenness in image quality, failing to solve the problem.
A method of preventing the error propagation without reduction in compression rate is disclosed, for example, in Japanese Patent Application No. 60-160599. In this method, among a plurality of non-linear quantizing units there is selected one unit whose quantization width in the vicinity of a predictive value is small, to perform the quantization. This method basically utilizes the direct quantization of input pixel values, not the quantization of differences. As a result, the predictive value error is hardly propagated. However, the construction provided with a plurality of quantizing units will increase its circuit scale, leading to the cost increase.